Coating compositions for roofing granules, dark colored roofing granules with increased solar heat reflectance, solar heat-reflective shingles and process for producing the same

ABSTRACT

Dark colored roofing granules include an inert base particle coated with a composition including a metal silicate, a non-clay latent heat reactant, and a dark colored but solar reflective pigment.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of pending U.S. applicationSer. No. 13/933,579, filed Jul. 2, 2013, which is a continuation of U.S.application Ser. No. 12/933,144, filed Sep. 17, 2010; which is a U.S.National Stage of U.S. Application No: PCT/US09/037467, filed Mar. 18,2009; which is a PCT of U.S. Provisional Application No. 61/040,983,filed Mar. 31, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to protective granules for asphalt roofingshingles, coating compositions for preparing roofing granules, roofinggranules, roofing shingles employing such granules, and processes formakings such granules and shingles.

2. Brief Description of the Prior Art

Pigment-coated mineral rocks are commonly used as color granules inroofing applications to provide aesthetic as well as protectivefunctions to the asphalt shingles. Roofing granules are generally usedin asphalt shingles or in roofing membranes to protect asphalt fromharmful ultraviolet radiation.

Roofing granules typically comprise crushed and screened mineralmaterials, which are subsequently coated with a binder containing one ormore coloring pigments, such as suitable metal oxides. The binder can bea soluble alkaline silicate that is subsequently insolubilized by heator by chemical reaction, such as by reaction between an acidic materialand the alkaline silicate, resulting in an insoluble colored coating onthe mineral particles. For example, U.S. Pat. No. 1,898,345 to Demingdiscloses coating a granular material with a coating compositionincluding a sodium silicate, a coloring pigment, and a colloidal clay,and heating below the fusing temperature of sodium silicate, andsubsequently treating with a solution, such as a solution of calcium ormagnesium chloride, or aluminum sulphate, that will react with thesodium silicate to form an insoluble compound. Similarly, U.S. Pat. No.2,378,927 to Jewett discloses a coating composition for roofing granulesconsisting of sodium silicate, and clay or another aluminum-bearingcompound such as sodium aluminate, or cryolite or other insolublefluorides such as sodium silicofluoride, and a color pigment. Thecoating is then heat cured at a temperature above the dehydrationtemperature of the coating materials but below the fusion temperature atwhich the combination of materials fuses, thus producing a non-porous,insoluble weather-resistant cement. Preparation of colored, coatedroofing granules is also disclosed for example, in U.S. Pat. No.2,981,636 of Lodge et al. The granules are employed to provide aprotective layer on asphaltic roofing materials such as shingles, and toadd aesthetic values to a roof.

Pigments for roofing granules have usually been selected to provideshingles having an attractive appearance, with little thought to thethermal stresses encountered on shingled roofs. However, depending onlocation and climate, shingled roofs can experience very challengingenvironmental conditions, which tend to reduce the effective servicelife of such roofs. One significant environmental stress is the elevatedtemperature experienced by roofing shingles under sunny, summerconditions, especially roofing shingles coated with dark colored roofinggranules. Although such roofs can be coated with solar reflective paintor coating material, such as a composition containing a significantamount of titanium dioxide pigment, in order to reduce such thermalstresses, this utilitarian approach will often prove to be aestheticallyundesirable, especially for residential roofs.

Mineral surfaced asphalt shingles, such as those described in ASTM D225or D3462, are generally used in steep-sloped roofs to providewater-shedding function while adding aesthetically pleasing appearanceto the roofs. The asphalt shingles are generally constructed fromasphalt-saturated roofing felts and surfaced by pigmented colorgranules, such as those described in U.S. Pat. No. 4,717,614. Asphaltshingles coated with conventional roofing granules are known to have lowsolar heat reflectance, and hence will absorb solar heat especiallythrough the near infrared range (700 nm-2500 nm) of the solar spectrum.This phenomenon is increased as the granules covering the surface becomedark in color. For example, while white-colored asphalt shingles canhave solar reflectance in the range of 25-35%, dark-colored asphaltshingles can only have solar reflectance of 5-15%. Furthermore, exceptin the white or very light colors, there is typically only a very smallamount of pigment in the conventional granule's color coating thatreflects solar radiation well. As a result, it is common to measuretemperatures as high as 77° C. on the surface of black roofing shingleson a sunny day with 21° C. ambient temperature. Absorption of solar heatmay result in elevated temperatures at the shingle's surroundings, whichcan contribute to the so-called heat-island effects and increase thecooling load to its surroundings. It is therefore advantageous to haveroofing shingles that have high solar reflectivity in order to reducethe solar heat absorption.

The surface reflectivity of an asphalt shingle largely depends on thesolar reflectance of the granules that are used to cover the bitumen.Roofing granules are typically produced by pigmenting inert mineralparticles with metal-silicate binders and clays as a latent heatreactant at an elevated temperature, for example, such as thosedescribed in U.S. Pat. No. 2,981,636.

In order to reduce the solar heat absorption, one may use light coloredroofing granules which are inherently more reflective towards the solarradiation. White pigment containing latex coatings have been proposedand evaluated by various manufacturers. However, consumers andhomeowners often prefer darker or earth tone colors for their roof. Inrecent years, there have been commercially available roofing granulesthat feature a reflective base coat (i.e., a white coat) and a partiallycoated top color coat allowing the reflective base coat to be partiallyrevealed to increase solar reflectance. Unfortunately, these granuleshave a “washed-out” color appearance due to the partially revealed whitebase coat.

Other manufactures have also proposed the use of exterior-grade coatingsthat were colored by infrared-reflective pigments for deep-tone colorsand sprayed onto the roof in the field. U.S. Patent ApplicationPublication No. 2003/0068469 A1 discloses an asphalt-based roofingmaterial comprising mat saturated with an asphalt coating and a topcoating having a top surface layer that has a solar reflectance of atleast 70%. U.S. Patent Application Publication No. 2003/0152747 A1discloses the use of granules with solar reflectance greater than 55%and hardness greater than 4 on the Moh's scale to enhance the solarreflectivity of asphalt based roofing products. However, there is nocontrol of color blends and the novel granules are typically availableonly in white or buff colors. U.S. Patent Application Publication No.2005/0074580 A1 discloses a non-white construction surface comprising afirst reflective coating and a second reflective coating with totaldirect solar reflectance of at least 20%.

Also, there have been attempts in using special near-infrared reflectivepigments in earth-tone colors to color roofing granules for increasedsolar reflectance. However, the addition of kaolin clays, which are usedto make the metal-silicate binder durable through heat curing,inevitably reduce the color strength or the color intensity of thepigment. As a result, dark-colored or black granules (L* less than 30)that have good solar reflectance (greater than 20 percent) cannot beproduced using conventional roofing granule manufacturing processes withclay as a latent reactant.

Colored roofing granules can also be prepared using a metal silicatebinder without adding clay and curing the binder at temperatures greaterthan glass sintering temperature, or through a “pickling” process byapplying acid. However, these alternatives require either very hightemperatures, or the use of corrosive chemicals, and in many cases couldresult in loss of color due to pigment degradation by the acid. In thealternative, a non-silicate binder, such as a synthetic polymericbinder, can be used to coat the inert mineral materials in order toproduce roofing granules with dark colors and high solar reflectance.However, the long-term durability and cost for polymeric coatings arenot as advantageous as the silicate binders.

Therefore, it would be advantageous to have a method of producingdark-colored roofing granules with high solar reflectance using ametal-silicate binder. There is a continuing need for roofing materials,and especially asphalt shingles, that have improved resistance tothermal stresses while providing an attractive appearance. Inparticular, there is a need for roofing granules that provide increasedsolar heat reflectance to reduce the solar absorption of the shingle,while providing a wide range of colors including deep-tone colors tomaintain the aesthetic value of the system.

SUMMARY OF THE INVENTION

The present invention provides a coating composition for preparingroofing granules, roofing granules that provide increased solar heatreflectance, while providing deep-tone colors, as well as a process forpreparing such roofing granules, and asphalt shingle roofing productsincorporating such roofing granules.

In one aspect, the present invention provides a coating composition forpreparing roofing granules. The coating composition comprises a metalsilicate, at least one non-clay latent heat reactant, at least one solarheat-reflective pigment; and optionally, at least one colorant.Preferably, the at least one non-clay latent heat reactant is selectedfrom the group consisting of Portland cement, aluminum fluoride,ammonium silicofluoride, alkali metal silicofluorides, and alkalineearth metal silicofluorides. More preferably, the at least one non-claylatent heat reactant comprises Portland cement, aluminum fluoride and atleast one alkali metal silicofluoride. Preferably, the at least onealkali metal silicofluoride is sodium silicofluoride. Preferably, the atleast one non-clay latent heat reactant comprise from about 3 to 15weight percent of the coating composition of aluminum fluoride, fromabout 0.5 to 5 weight percent of the coating composition of sodiumsilicofluoride, and from about 0.5 to 5 weight percent of the coatingcomposition of Portland cement. More preferably, the at least onenon-clay latent heat reactant comprise from about 5 to 11 weight percentof the coating composition of aluminum fluoride, from about 1.5 to 3weight percent of the coating composition of sodium silicofluoride, andfrom about 1.5 to 3 weight percent of the coating composition ofPortland cement. Preferably, the metal silicate is selected from thegroup consisting of ammonium silicate, sodium silicate, potassiumsilicate and lithium silicate. Preferably, the at least one solarheat-reflective pigment is selected from the group consisting of solarreflective pigments having an L* less than 30 and a solar reflectancegreater than 20 percent.

In another aspect, the present invention provides dark colored,solar-heat reflective roofing granules. The roofing granules accordingto the present invention comprise an inert base particle and at leastone coating layer. The at least one coating layer is formed from asilicate coating composition comprising a metal silicate coating bindercomprising a metal silicate and at least one non-clay latent heatreactant, at least one solar-heat reflective pigment; and at least onecolorant. Preferably, the at least one solar-heat reflective pigment andthe at least one colorant are selected to provide roofing granuleshaving an L* less than 30 and solar reflectance of at least 20 percent.Preferably, the at least one non-clay latent heat reactant is selectedfrom the group consisting of Portland cement, aluminum fluoride,ammonium silicofluoride, alkali metal silicofluorides, and alkalineearth metal silicofluorides. More preferably, the at least one non-claylatent heat reactant comprises Portland cement, aluminum fluoride and atleast one alkali metal silicofluoride. Preferably, the at least onealkali metal silicofluoride is sodium silicofluoride. Preferably, the atleast one non-clay latent heat reactant comprises from about 3 to 15weight percent of the coating composition of aluminum fluoride, fromabout 0.5 to 5 weight percent of the coating composition of sodiumsilicofluoride, and from about 0.5 to 5 weight percent of the coatingcomposition of Portland cement. More preferably, the at least onenon-clay latent heat reactant comprises from about 5 to 11 weightpercent of the coating composition of aluminum fluoride, from about 1.5to 3 weight percent of the coating composition of sodium silicofluoride,and from about 1.5 to 3 weight percent of the coating composition ofPortland cement. Preferably, the metal silicate is selected from thegroup consisting of ammonium silicate, sodium silicate, potassiumsilicate and lithium silicate. Preferably, the at least one solarreflective pigment is selected from the group consisting of solarreflective pigments having L* less than 30 and a solar reflectance of atleast 20 percent. In one embodiment, the roofing granules of the presentinvention comprise at least two coating layers formed from the silicatecoating composition. It is preferred that the at least one solarreflective pigment comprises from about 1 percent by weight to about 60percent by weight of the coating composition in which it is dispersed.Preferably, the coating composition comprises from about 2 percent byweight of the base particles to about 20 percent by weight of the baseparticles. More preferably, the coating composition comprises from about4 percent by weight of the base particles to about 10 percent by weightof the base particles.

In yet another aspect, the present invention provides roofing shinglescomprising dark colored, solar reflective roofing granules according tothe present invention.

In another aspect, the present invention provides a method of makingroofing granules. This method comprises providing inert base particles,coating the inert base particles with a coating composition according tothe present invention to form at least one coating layer on the inertbase particles, and curing the coating composition at an elevatedtemperature less than the glass sintering temperature of silica.Preferably, the elevated temperature is greater than the dehydrationtemperature of the components of the coating composition. Preferably,the coating composition is cured between about 300 degrees F. (149degrees C.) and 1100 degrees F. (593 degrees C.). More preferably, thecoating composition is cured between about 500 degrees F. (260 degreesC.) and 1000 degrees F. (538 degrees C.). Preferably, at least twocoating layers are formed in preparing the roofing granules.

The process of the present invention produces coloredinfrared-reflective roofing granules that have a higher solar heatreflectance than colored roofing granules prepared using conventionalmetal oxide colorants, which typically have a solar heat reflectance offrom about 12 percent to about 20 percent. Thus, it is preferred thatthe colored infrared-reflective roofing granules of the presentinvention have a solar heat reflectance greater than about 20 percent.It is especially preferred that the colored infrared-reflective roofinggranules according to the present invention have a solar heatreflectance of at least about 25 percent, and that bituminous roofingproducts, such as asphaltic roofing shingles, made with such coloredinfrared-reflective roofing granules have a solar heat reflectance of atleast about 20 percent, more preferably at least about 25 percent, witha solar heat reflectance of at least about 30 percent being especiallypreferred.

The solar-reflective granules of the present invention can be preparedby pre-mixing the components of the infrared-reflective coating, namelythe binder, pigment(s), and optional additives to a slurry consistency,followed by uniform mixing with the base particles, such as mixing in arotary tumbler, to achieve a uniform coating on the base particles. Theweight of the solar reflective coating composition is preferably fromabout 2% by weight to about 20% of the weight of the base particles,more preferably from about 4% by weight to about 10% by weight of thebase particles. After the mixing, the coated granules can be dried in arotary drum or fluidized bed with suitable heat to cure theinfrared-reflective coating. Alternatively, the base particles can bespray-coated by the pre-mixed solar reflective coating composition in arotary drum to achieve uniform coverage, followed by drying to achieve adurable solar reflective coating.

After the preparation of the granules to reach desirable colors,particularly in the mid to deep tone colors, the granules can then bedeposited onto the asphalt shingle surface during the shinglemanufacturing to enhance the solar heat reflectance of the finalproduct.

The present invention also provides a process for producing solarreflective roofing shingles, as well as the shingles themselves. Thisprocess comprises producing solar reflective roofing granules using theprocess of this invention, and adhering the granules to a shingle stockmaterial.

The dark colored, solar reflective roofing granules prepared accordingto the process of the present invention can be employed in themanufacture of solar reflective roofing products, such as solarreflective asphalt shingles and roll goods, including bituminousmembrane roll goods. The dark colored, solar reflective granules of thepresent invention can be mixed with conventional roofing granules, andthe granule mixture can be embedded in the surface of bituminous roofingproducts using conventional methods. Alternatively, the colored, solarreflective granules of the present invention can be substituted forconventional roofing granules in manufacture of bituminous roofingproducts, such as asphalt roofing shingles, to provide those roofingproducts with solar reflectance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a dark colored roofing granuleaccording a first embodiment of the present invention.

FIG. 2 is a schematic representation of a dark colored roofing granuleaccording a second embodiment of the present invention.

FIG. 3 is a schematic representation of a dark colored roofing granuleaccording a third embodiment of the present invention.

DETAILED DESCRIPTION

The present invention provides coating compositions based uponmetal-silicate binders and pigment combinations for producing novelroofing granules having a luminance L* less than 30 and solarreflectance at least 20 percent.

As used in the present specification and claims, L*, a* and b* refer tothe parameters of the CIELAB color system. As used in the presentspecification and claims, “colored” means having an L* value of lessthan 85, preferably less than 55, even more preferably less than 45,when measured using a HunterLab Model Labscan XE spectrophotometer usinga 0 degree viewing angle, a 45 degree illumination angle, a 10 degreestandard observer, and a D-65 illuminant. “Colored” as so defined isintended to include relatively dark tones. As using in the presentspecification and claims, “dark color” means a color having an L* valueless than about 30. As used in the present specification and claims,“solar reflective,” and “solar heat-reflective” refer to reflectance inthe near infrared range (700 to 2500 nm) of the electromagneticspectrum, and “high solar reflectance” means having an averagereflectance of at least about 70 percent over the near infrared range(700 to 2500 nm) of the electromagnetic spectrum. As used in the presentspecification as claims, “solar reflective functional pigment” denotes apigment selected from the group consisting of light-interferenceplatelet pigments including mica, light-interference platelet pigmentsincluding titanium dioxide, mirrorized silica pigments based uponmetal-doped silica, metal flake pigments, metal oxide coated flakepigments, and alumina. As used in the present specification and claims,“granule coloring pigment” denotes a conventional metal oxide-typepigment employed to color roofing granules.

The coating compositions of the present invention can be achieved byadding solar-reflective pigments to metal silicate binders and renderingthe metal silicate binder insoluble using non-clay latent heatreactants. Such latent heat reactants for metal-silicate binders areknown to exist in coating industry, for example (and included herein asreference), U.S. Pat. No. 4,717,614 teaches the art of preparingmetal-silicate coatings using multivalent metal ions. However, theresultant coatings do not have the necessary outdoor long termdurability for roofing applications and oftentimes can cure too fastwithout sufficient working time for the coating composition to be pumpedand applied onto the mineral rocks in a roofing granule plant setting.

In the present invention, fluorinated aluminum compounds having certainsolubility in metal-silicate solutions and Portland cement can be usedto insolubilize the silicate coating at temperatures significantly belowthe glass sintering temperature of the coating composition. Inparticular, the combination of aluminum fluoride, sodium silicofluoride,and Portland cement reacted at temperatures above the dehydrationtemperature of the coating composition and below the sinteringtemperature of the coating composition can result in a long-term durablesilicate coating as confirmed by conventional roofing granule industrytesting. To achieve a dark color (L* less than 30) and high solarreflectance, infrared-reflective pigments that are specially engineeredto reflect solar radiation in the near-infrared spectrum can bedispersed in the coating compositions. These pigments are commerciallyavailable from, for example, Ferro Corp., Cleveland, Ohio; or ShepherdColor Company, Cincinnati, Ohio). Also, reflective fillers such asmirrorized silica flakes, metal flakes, or metal oxide coated flakes canbe added to the coating compositions. Further, plural coating layersformed from coating compositions having different color pigmentsdispersed in the metal silicate binder can be used to achieve thedesirable color space and solar reflectance. Further, biocides,particles with photo-catalytic effects, or other functional additivescan be dispersed in the coating composition to incorporate furtherfunctionalities.

The roofing granule coating compositions of the present invention can beprepared through traditional methods, such as those disclosed in U.S.Pat. Nos. 2,378,927, 2,695,851, and 2,981,636, each incorporated hereinby reference.

The coating binder employed in the process of the present invention toform the coating composition is preferably formed from a mixture of analkali metal silicate, such as aqueous sodium silicate, and at least onenon-clay latent heat reactant. As used in the present specification andclaims, by “latent heat reactant” is meant a material that chemicallyreacts with a metal silicate at a temperature less than the glasssintering temperature of the coating composition to form an insolublematerial. When an aqueous solution of a metal silicate, such as anaqueous solution of an alkali metal silicate such as water glass isemployed, the latent heat reactant is preferably selected to reactchemically with the metal silicate at a temperature greater than thedehydration temperature of the coating composition, but which is lessthan the glass sintering temperature of the coating composition.

The metal silicate binder employed in the coating compositions of thepresent invention is preferably an aqueous ammonium silicate or aqueousalkali metal silicate, such as, for example, ammonium silicate, sodiumsilicate, potassium silicate, and lithium silicate. Preferably, themetal silicate employed in the coating compositions of the presentinvention is aqueous sodium silicate (water glass). The composition ofaqueous sodium silicate is typically characterized by the weight ratioof silicon dioxide to sodium oxide. Preferably, the aqueous sodiumsilicate employed in the coating compositions of the present inventionhave a weight ratio of silicon dioxide to sodium oxide of from about3.25:1 to 2:1, and a total solids content of from about 38 percent byweight to about 42 percent by weight.

The coating compositions of the present invention preferably comprise atleast one non-clay latent heat reactant. Examples of non-clay latentheat reactant that can be employed in preparing the coating compositionsof the present invention include fluoride compounds such as aluminumfluoride, gallium fluoride, indium fluoride, sodium fluoride, potassiumfluoride, lithium fluoride, sodium silicofluoride, ammoniumsilicofluoride, potassium silicofluoride, lithium silicofluoride, bariumsilicofluoride, zinc silicofluoride, and magnesium silicofluoride, aswell as fluoride containing minerals such as cryolite. Further examplesof non-clay latent heat reactants include hydraulic cements such asPortland cements, such as Type I Portland cement and Type III Portlandcement, blended Portland cements, such as blends of Portland cement withblast furnace slag, blends of Portland cement with pozzolanic materialssuch as fly ash, expansive Portland cements such as Types K, M, S and Ocements, rapid setting and rapid hardening Portland cements such asregulated set cement, very high early strength cement, high iron cement,and ultra high early strength cement, low-tricalcium aluminate cementssuch as API class A, C, D, E and F cements, calcium aluminate cements,as well as Portland cement constituents including tricalcium silicate,beta-dicalcium silicate, alite and belite.

Preferably, the at least one non-clay latent heat reactant comprisesaluminum fluoride, an alkali metal silicofluoride, and Portland cement.Preferably, the at least one non-clay latent heat reactant comprisesfrom about 3 to 15 weight percent of the coating composition of aluminumfluoride, from about 0.5 to 5 weight percent of the coating compositionof sodium silicofluoride, and from about 0.5 to 5 weight percent of thecoating composition of Portland cement. More preferably, wherein the atleast one non-clay latent heat reactant comprises from about 5 to 11weight percent of the coating composition of aluminum fluoride, fromabout 1.5 to 3 weight percent of the coating composition of sodiumsilicofluoride, and from about 1.5 to 3 weight percent of the coatingcomposition of Portland cement.

The proportion of alkali metal silicate to the at least one non-claylatent heat reactant is preferably from about 4:1 to about 1.3:1 partsby weight alkali metal silicate to parts by weight non-clay latent heatreactant, more preferably about 3:1 to about 1.5:1 parts by weightalkali metal silicate to parts by weight at least one non-clay latentheat reactant.

The coating compositions of the present invention also include at leastone solar reflective pigment. Examples of solar reflective pigments thatcan be employed in the coating compositions of the present inventioninclude near infrared-reflective pigments available from the ShepherdColor Company, Cincinnati, Ohio, including Arctic Black 10C909 (chromiumgreen-black), Black 411 (chromium iron oxide), Brown 12 (zinc ironchromite), Brown 8 (iron titanium brown spinel), and Yellow 193 (chromeantimony titanium), as well as near infrared reflective pigmentsavailable from the Ferro Corporation (Cincinnati, Ohio), such as Brown10364, Eclipse Black 10201, IR BRN Black V-780, Forest Green 10241, BlueV-9248, Bright Blue V-9250, Turquoise F05686, Eclipse Black 10202,Eclipse Black 10203, Red V-13810, IR Cobalt Green V-12600, H IR GreenV-12650, IR Brown Black V-778, and Brown Black V-799.

The dark colored, solar reflective pigment employed in the coatingcompositions of the present invention can comprise a solid solutionincluding iron oxide, such as disclosed in U.S. Pat. No. 6,174,360,incorporated herein by reference. The colored solar reflective pigmentcan also comprise a near infrared-reflecting composite pigment such asdisclosed in U.S. Pat. No. 6,521,038, incorporated herein by reference.Composite pigments are composed of a near-infrared non-absorbingcolorant of a chromatic or black color and a white pigment coated withthe near infrared-absorbing colorant.

Preferably, the at least one solar reflective pigment comprises fromabout 1 percent by weight to about 60 percent by weight of the coatingcomposition; more preferably from about 5 to 25 percent by weight of thecoating composition, and still more preferably from about 7 to 15percent by weight of the coating composition.

The coating composition can also include at least one solar reflectivefunctional pigment. Examples of solar reflective functional pigmentsinclude light-interference platelet pigments, mirrorized silicapigments, metal flake pigments, metal oxide coated flake pigments, andalumina.

Light-interference platelet pigments are known to give rise to variousoptical effects when incorporated in coatings, including opalescence or“pearlescence.” Surprisingly, light-interference platelet pigments havebeen found to provide or enhance infrared-reflectance of roofinggranules coated with compositions including such pigments.

Examples of light-interference platelet pigments that can be employed inthe process of the present invention include pigments available fromWenzhou Pearlescent Pigments Co., Ltd., No. 9 Small East District,Wenzhou Economical and Technical Development Zone, Peoples Republic ofChina, such as Taizhu TZ5013 (mica, rutile titanium dioxide and ironoxide, golden color), TZ5012 (mica, rutile titanium dioxide and ironoxide, golden color), TZ4013 (mica and iron oxide, wine red color),TZ4012 (mica and iron oxide, red brown color), TZ4011 (mica and ironoxide, bronze color), TZ2015 (mica and rutile titanium dioxide,interference green color), TZ2014 (mica and rutile titanium dioxide,interference blue color), TZ2013 (mica and rutile titanium dioxide,interference violet color), TZ2012 (mica and rutile titanium dioxide,interference red color), TZ2011 (mica and rutile titanium dioxide,interference golden color), TZ1222 (mica and rutile titanium dioxide,silver white color), TZ1004 (mica and anatase titanium dioxide, silverwhite color), TZ4001/600 (mica and iron oxide, bronze appearance),TZ5003/600 (mica, titanium oxide and iron oxide, gold appearance),TZ1001/80 (mica and titanium dioxide, off-white appearance), TZ2001/600(mica, titanium dioxide, tin oxide, off-white/gold appearance),TZ2004/600 (mica, titanium dioxide, tin oxide, off-white/blueappearance), TZ2005/600 (mica, titanium dioxide, tin oxide,off-white/green appearance), and TZ4002/600 (mica and iron oxide, bronzeappearance).

Examples of light-interference platelet pigments that can be employed inthe process of the present invention also include pigments availablefrom Merck KGaA, Darmstadt, Germany, such as Iriodin® pearlescentpigment based on mica covered with a thin layer of titanium dioxideand/or iron oxide; Xirallic™ high chroma crystal effect pigment basedupon aluminum oxide platelets coated with metal oxides, includingXirallic T 60-10 WNT crystal silver, Xirallic T 60-20 WNT sunbeam gold,and Xirallic F 60-50 WNT fireside copper; ColorStream™ multi coloreffect pigments based on SiO2 platelets coated with metal oxides,including ColorStream F 20-00 WNT autumn mystery and ColorStream F 20-07WNT viola fantasy; and ultra interference pigments based on titaniumdioxide and mica.

Examples of mirrorized silica pigments that can be employed in theprocess of the present invention include pigments such as Chrom Brite™CB4500, available from Bead Brite, 400 Oser Ave, Suite 600, Hauppauge,N.Y. 11788.

Aluminum oxide, preferably in powdered form, can be used assolar-reflective additive in the color coating formulation to improvethe solar reflectance of colored roofing granules without affecting thecolor. The aluminum oxide should have particle size less than U.S. #40mesh (425 micrometer), preferably between 0.1 micrometer and 5micrometer. More preferably, the particle size is between 0.3 micrometerand 2 micrometer. The alumina should have percentage aluminumoxide >90%, more preferably >95%.

Examples of metal flake pigments include aluminum flake pigments, ironflake pigments, iron-aluminum alloy flake pigments, copper flakepigments, brass flake pigments, titanium flake pigments,iron-cobalt-aluminum alloy flake pigments, stainless steel flakepigments, chromium flake pigments, nickel flake pigments, and nickelalloy flake pigments. Examples of metal oxide coated flake pigments aredisclosed, for example, in U.S. Pat. No. 6,589,331.

The coating compositions of the present invention can includeconventional coatings pigments. Examples of coatings pigments that canbe used include those provided by the Color Division of FerroCorporation, 4150 East 56th St., Cleveland, Ohio 44101, and producedusing high temperature calcinations, including PC-9415 Yellow, PC-9416Yellow, PC-9158 Autumn Gold, PC-9189 Bright Golden Yellow, V-9186Iron-Free Chestnut Brown, V-780 Black, V0797 IR Black, V-9248 Blue,PC-9250 Bright Blue, PC-5686 Turquoise, V-13810 Red, V-12600 CamouflageGreen, V12560 IR Green, V-778 IR Black, and V-799 Black. Furtherexamples of coatings pigments that can be used include white titaniumdioxide pigments provided by Du Pont de Nemours, P.O. Box 8070,Wilmington, Del. 19880.

The coating composition of the present invention is applied to basemineral particles to provide a layer of the coating composition on thebase particle. The coating composition is then cured at an elevatedtemperature, preferably at a temperature above the dehydrationtemperature of the coating composition but less than the sinteringtemperature of the coating composition to provide an insoluble coatinglayer on the base particle. Such a coating process can be repeated toform multiple coatings to further enhance the color and solarreflection. Thus, a second, third or more layers of pigmented coatingcan be applied in like manner. The second, third, or further layers canbe formed from a coating composition which has the same composition asthe coating composition employed to form the initial layer. In addition,the composition of the coating composition of the second, third, orfurther layers can differ from the composition of coating compositionused for the initial layer. For example, the pigment composition of thesecond layer can differ from the pigment composition of the first layer.For example, the pigment composition of the first layer and the secondlayer can be selected to provide desired values of color spacecoordinates (hue, chroma, and lightness) and solar reflectance for eachlayer and for the resulting multi-layer coating.

Preferably, the solar reflective coating is provided in a thicknesseffective to render the coating opaque to infrared radiation, such as acoating thickness of at least about 100 micrometers. However,advantageous properties of the present invention can be realized withsignificantly lower coating thicknesses, such as at a coating thicknessof from about 2 micrometers to about 25 micrometers including at acoating thickness of about 5 micrometer. Preferably, when plural coatinglayers are employed, each coating layer has a thickness of at leastabout 2 micrometers.

The solar heat reflectance properties of the solar heat-reflectiveroofing granules of the present invention are determined by a number offactors, including the type and concentration of the solar reflectivepigment(s) used in the solar heat-reflective coating composition,whether multiple coating layers are provided, and if so, the type andconcentration of the solar reflective pigment employed in each coatinglayer, the nature of the binder(s) used in for the solar heat-reflectivecoating and the base coating, the number of coats of solarheat-reflective coating employed, the thickness of the solar reflectivecoating layers, and the size and shape of the base particles.

Infrared-reflective coating compositions according to the presentinvention can also include supplementary pigments to spaceinfrared-reflecting pigments, to reduce absorption bymultiple-reflection. Examples of such “spacing” pigments includeamorphous silicic acid having a high surface area and produced by flamehydrolysis or precipitation, such as Aerosil TT600 supplied by Degussa,as disclosed in U.S. Pat. No. 5,962,143, incorporated herein byreference.

The coating composition of the present invention can also include othertypes of functional additives, such as additive to provide resistance toalgae growth. Examples of suitable algae growth inhibitors aredisclosed, for example, in U.S. Patent Application Publications Nos.2004/0255548 A1 and 2004/0258835 A1, each incorporated herein byreference.

It is preferred that the coating composition comprises from about 2percent by weight of the base particles to about 20 percent by weight ofthe base particles. More preferably, the coating composition comprisesfrom about 4 percent by weight of the base particles to about 10 percentby weight of the base particles.

Suitable inert base particles, for example, mineral particles with sizepassing U.S. #8 mesh and retaining on U.S. #70 mesh, can be coated withone or more layers of coating compositions according to the presentinvention to reach desirable colors and solar reflectance to obtain adurable coating.

The inert base particles employed in the process of the presentinvention are preferably chemically inert materials, such as inertmineral particles. The mineral particles, which can be produced by aseries of quarrying, crushing, and screening operations, are generallyintermediate between sand and gravel in size (that is, between about #8U.S. mesh and #70 U.S. mesh), and preferably have an average particlesize of from about 0.2 mm to about 3 mm, and more preferably from about0.4 mm to about 2.4 mm.

In particular, suitably sized particles of naturally occurring materialssuch as talc, slag, granite, silica sand, greenstone, andesite,porphyry, marble, syenite, rhyolite, diabase, greystone, quartz, slate,trap rock, basalt, and marine shells can be used, as well asmanufactured or recycled manufactured materials such as crushed bricks,concrete, porcelain, fire clay, and the like.

In one set of presently preferred embodiments, the inert base particlescomprise particles having a generally plate-like geometry. Examples ofgenerally plate-like particles include mica and flaky slate. Coloredroofing granules having a generally plate-like geometry have been foundto provide greater surface coverage when used to prepare bituminousroofing products, when compared with conventional “cubical” roofinggranules, as shown in Table A below. Granule surface coverage ismeasured using image analysis software, namely, Image-Pro Plus fromMedia Cybernetics, Inc., Silver Spring, Md. 20910. The shingle surfacearea is recorded in a black and white image using a CCD camera fitted toa microscope. The image is then separated into an asphalt coatingportion and a granule covering portion using the threshold method ingray scale. The amount of granule coverage is then calculated by theimage analysis software based upon the number of pixels with gray scaleabove the threshold level divided by the total number of pixels in theimage.

TABLE A Sample Color Granule Type Surface Coverage % A White cubical86.0 B Wood Blend cubical 86.6 C Natural flaky slate 91.6 D Naturalflaky slate 92.1 E Natural flaky slate 92.9 F Natural flaky slate 91.8

The process of the present invention for producing solar reflectiveroofing granules comprises several steps. In one step of the presentprocess, a coating composition according to the present invention isprepared by mixing a suitable metal silicate such as aqueous sodiumsilicate with the at least one non-clay latent heat reactant, such as amixture of aluminum fluoride, sodium silicofluoride, and Type I Portlandcement, and at least one suitable solar reflective pigment, preferably asolar reflective pigment selected to provide roofing granules having L*less than 30 and a solar reflectance of at least 20 percent, such asFerro Eclipse® Black 10202. In another step of the process of producingsolar reflective roofing granules according to the present invention,suitable base particles are provided. These can be suitably sized,chemically inert, mineral particles. The base particles are then coatedusing the coating composition of the present invention to form a coatinglayer on the base particles. The coating composition is dried at lowtemperature, such as by drying in a fluidized bed drier. Next, thecoating composition is cured at an elevated temperature, preferablygreater than the dehydration temperature of the coating composition, butless than the sintering temperature of the coating composition to form ahard, weather-resistant non-porous coating layer on the base particles.A second layer, and a third and further layers, can be applied in likemanner. Preferably, the coating composition forms a single layer having,or plural layers collectively having, sufficient thickness to providegood hiding and opacity, such as a thickness of from about 5 micrometersto about 50 micrometers.

Referring now to the figures in which like reference numerals representlike element in each of the several views, there is shown in FIG. 1, aschematic illustration of the structure of a dark colored solarreflective roofing granule 10 according to a presently preferred firstembodiment of the present invention. The colored infrared-reflectiveroofing granule 10 includes a base particle 12 coated with a curedcoating composition 14 comprising a coating binder 16 and at least onesolar reflective pigment 18. The cured coating composition 14 isprepared by heat treatment of a coating composition according to thepresent invention, wherein the coating binder 16 is prepared from amixture including sodium silicate, aluminum fluoride, sodiumsilicofluoride, and Portland cement. Preferably, in the dark colored,solar reflective roofing granules 10, the solar reflective pigment 18comprises from about 1 percent by weight to about 60 percent by weightof the coating composition 14. Preferably, the cured coating composition14 comprises from about 2 percent by weight of the base particles 12 toabout 20 percent by weight of the base particles 12. More preferably,the cured coating composition 14 comprises from about 4 percent byweight of the base particles 12 to about 10 percent by weight of thebase particles 12. Optionally, the coating composition 14 can include atleast one coloring material selected from the group consisting ofgranule coloring pigments and algaecides.

Thus, in this first embodiment of dark colored solar reflecting roofinggranules 10 of the present invention, the solar reflectance and thecolor of the dark colored roofing granules 10 are attributable to thecolored, solar reflective pigment 18.

FIG. 2 is a schematic illustration of the structure of a dark coloredsolar reflective roofing granule 20 according to a presently preferredsecond embodiment of the present invention. In this embodiment, roofinggranule 20 includes a base particle 22 comprising a mineral particle 24coated with a cured base coating composition 26 according to the presentinvention including a base particle binder 28, and at least one solarreflective pigment 30 to form an initial coating layer. It is preferredthat the at least one solar reflective pigment 30 comprises from about 5percent by weight to about 60 percent by weight of the base coatingcomposition 26, and more preferred that the at least one solarreflective pigment 30 comprises from about 30 percent by weight to about40 percent by weight of the base coating composition 26. In thisembodiment, the base coating composition 26 preferably comprises fromabout 1 percent by weight of the inert mineral particles 22 to about 20percent by weight of the inert mineral particles 24, and morepreferably, from about 4 percent by weight of the base particles toabout 10 percent by weight of the inert mineral particles. The baseparticle binder 28 preferably an alkali metal silicate and at least onenon-clay latent heat reactant, preferably a mixture consisting ofaluminum fluoride, sodium silicofluoride, and Portland cement. The darkcolored solar reflective roofing granules 20 of this second embodimentinclude a second, cured coating composition 40, comprising a coatingbinder 42, and at least one colored, solar reflective pigment 44. Inthis embodiment, the composition of the second coating composition 40 isthe same as the first coating composition 26. The cured second coatingcomposition 40 forms a second layer of identical composition to thecured coating composition 26 forming the initial coating layer on themineral particle 24.

In this second embodiment of colored roofing granules 20 of the presentinvention, both the color and the solar reflectance of the coloredroofing granules 30 are attributable to both the solar reflectivepigment 30 in the inner layer of the cured base coating composition 26,and the identical solar reflective pigment 44 in the outer layer of thecured coating composition 40. Adding the second coating layer increasesthe depth of the color and the solar reflectance of the roofinggranules. Optionally, a third layer of the same coating composition canbe applied to further enhance the depth of color and solar reflectanceof the roofing granules 20 (not shown).

FIG. 3 is a schematic illustration of the structure of a colored solarreflective roofing granule 50 according to a presently preferred thirdembodiment of the present invention. In this embodiment, the darkcolored solar reflective roofing granules 50 comprise base particles 52comprising inert mineral particles 54 coated with a cured first coatingcomposition 56 according to the present invention including a first orbase particle binder 58 and at least one solar reflective pigment 60 toform a first or inner layer on the mineral particles 54, and the baseparticles 52 are coated with a cured second coating composition 62according to the present invention including a second or outer coatingbinder 64, and at least one solar reflective pigment 66 and at least onesolar reflective functional pigment 68 to form a second or outer layeron the mineral particles 54. The at least one solar reflective pigment60 in the inner layer formed by the cured first coating composition 56differs from the at least one solar reflective pigment 66 in the outerlayer formed by the cured second coating composition 62 with respect tocolor space coordinates.

Preferably, in the colored infrared-reflective roofing granules 50 theat least one solar reflective pigment 66 comprises from about 1 percentby weight to about 60 percent by weight of the cured second coatingcomposition 62. In the colored infrared-reflective roofing granules 50of the third embodiment, the second coating composition 62 preferablyfurther comprise at least one solar reflective functional pigment 68selected from the group consisting of mirrorized silica flake pigments,metal flake pigments, and metal oxide coated flake pigments, and the atleast one solar reflective functional pigment 68 preferably comprisesfrom about 1 percent by weight to about 60 percent by weight of thesecond coating composition 62. In this third embodiment, the secondcoating composition 62 comprises from about 2 percent by weight of thebase particles 52 to about 20 percent by weight of the base particles52, more preferably, from about 4 percent by weight of the baseparticles 52 to about 10 percent by weight of the base particles 52. Inthis third embodiment, the first or base coating composition 56preferably comprises from about 1 percent by weight of the inert mineralparticles 54 to about 20 percent by weight of the inert mineralparticles 54. In this third embodiment, both the base particle binder 58and the second or outer coating binder 64 are clay-free coatingcompositions according to the present invention. Alternatively, one ofthe binders 58, 64 can comprise a conventional roofing granule coatingbinder comprising an aluminosilicate material and an alkali metalsilicate, where the aluminosilicate material is a clay such as kaolin.

Thus, in this third embodiment of dark colored solar reflective roofinggranules 50 according to the present invention, the solar reflectance ofthe colored roofing granules 50 is attributable to both of the differentsolar reflective pigments 60, 66 in the inner layer and outer layersform by the first and second coating compositions 56, 62, as well as tothe solar reflective functional pigment 68 in the outer layer formed bythe cured second coating composition 62. Similarly, the color of thegranules 50 of this third embodiment is a function of all three pigments60, 66, 68 dispersed in the first and second coating compositions 56,62.

The present invention provides mineral surfaced asphalt shingles with L*less than 55, and more preferably less than 30, and solar reflectancegreater than 20 percent. Preferably, asphalt shingles according to thepresent invention comprise colored, solar reflective granules accordingto the present invention, and optionally, conventional colored roofinggranules. Conventional colored roofing granules and infrared-reflectiveroofing granules can be blended in combinations to generate desirablecolors. The blend of granules is then directly applied on to hot asphaltcoating to form the shingle. Examples of granule deposition apparatusthat can be employed to manufacture asphalt shingles according to thepresent invention are provided, for example, in U.S. Pat. Nos.4,583,486, 5,795,389, and 6,610,147, and U.S. Patent ApplicationPublication U.S. 2002/0092596.

The process of the present invention advantageously permits the solarreflectance of the shingles employing the solar-reflective granules tobe tailored to achieve specific color effects.

The colored, infrared-reflective granules prepared according to theprocess of the present invention can be employed in the manufacture ofinfrared-reflective roofing products, such as infrared-reflectiveasphalt shingles, using conventional roofing production processes.Typically, bituminous roofing products are sheet goods that include anon-woven base or scrim formed of a fibrous material, such as a glassfiber scrim. The base is coated with one or more layers of a bituminousmaterial such as asphalt to provide water and weather resistance to theroofing product. One side of the roofing product is typically coatedwith mineral granules to provide durability, reflect heat and solarradiation, and to protect the bituminous binder from environmentaldegradation. The colored, infrared-reflective granules of the presentinvention can be mixed with conventional roofing granules, and thegranule mixture can be embedded in the surface of such bituminousroofing products using conventional methods. Alternatively, the colored,infrared-reflective granules of the present invention can be substitutedfor conventional roofing granules in manufacture of bituminous roofingproducts to provide those roofing products with solar reflectance.

Bituminous roofing products are typically manufactured in continuousprocesses in which a continuous substrate sheet of a fibrous materialsuch as a continuous felt sheet or glass fiber mat is immersed in a bathof hot, fluid bituminous coating material so that the bituminousmaterial saturates the substrate sheet and coats at least one side ofthe substrate. The reverse side of the substrate sheet can be coatedwith an anti-stick material such as a suitable mineral powder or a finesand. Roofing granules are then distributed over selected portions ofthe top of the sheet, and the bituminous material serves as an adhesiveto bind the roofing granules to the sheet when the bituminous materialhas cooled. The sheet can then be cut into conventional shingle sizesand shapes (such as one foot by three feet rectangles), slots can be cutin the shingles to provide a plurality of “tabs” for ease ofinstallation and aesthetic effect, additional bituminous adhesive can beapplied in strategic locations and covered with release paper to providefor securing successive courses of shingles during roof installation,and the finished shingles can be packaged. More complex methods ofshingle construction can also be employed, such as building up multiplelayers of sheet in selected portions of the shingle to provide anenhanced visual appearance, or to simulate other types of roofingproducts. Alternatively, the sheet can be formed into membranes or rollgoods for commercial or industrial roofing applications.

The bituminous material used in manufacturing roofing products accordingto the present invention is derived from a petroleum-processingby-product such as pitch, “straight-run” bitumen, or “blown” bitumen.The bituminous material can be modified with extender materials such asoils, petroleum extracts, and/or petroleum residues. The bituminousmaterial can include various modifying ingredients such as polymericmaterials, such as SBS (styrene-butadiene-styrene) block copolymers,resins, flame-retardant materials, oils, stabilizing materials,anti-static compounds, and the like. Preferably, the total amount byweight of such modifying ingredients is not more than about 15 percentof the total weight of the bituminous material. The bituminous materialcan also include amorphous polyolefins, up to about 25 percent byweight. Examples of suitable amorphous polyolefins include atacticpolypropylene, ethylene-propylene rubber, etc. Preferably, the amorphouspolyolefins employed have a softening point of from about 130 degrees C.to about 160 degrees C. The bituminous composition can also include asuitable filler, such as calcium carbonate, talc, carbon black, stonedust, or fly ash, preferably in an amount from about 10 percent to 70percent by weight of the bituminous composite material.

The following examples are provided to better disclose and teachprocesses and compositions of the present invention. They are forillustrative purposes only, and it must be acknowledged that minorvariations and changes can be made without materially affecting thespirit and scope of the invention as recited in the claims that follow.

In the examples, granule color measurements were made using the RoofingGranules Color Measurement Procedure from the Asphalt RoofingManufacturers Association (ARMA) Granule Test Procedures Manual, ARMAForm No. 441-REG-96.

EXAMPLE 1

Inert mineral rocks with sizes between U.S. #10 U.S. mesh and #40 U.S.mesh (commercially available from CertainTeed Corp., Piedmont, Mo.) arecoated by coating comprising 9.5 g sodium silicate binder (Grade 40from, Occidental Chemical Company, Dallas, Tex.), aluminum fluoride(available from Aldrich Chemical), sodium silicofluoride (available fromAldrich Chemical), kaolin clay (available from Unimin Corp.), andPortland cement as latent heat reactants in various combinations. Thedetails of the compositions are listed in Table 1. The coatingcomposition is first mixed in a beaker using a propeller mixer at 300rpm and then is blended with 25.0 g of the mineral particles until auniform mixture is achieved. The coated granules are then spread out onwax paper and dried in air. The granules are then placed in a crucibleand heat treated in a temperature-controlled furnace set at 260 degreesC. (500 degrees F.) or 538 degrees C. (1000 degrees F.) for 3 hours. Thegranules are then cooled to room temperature, and their surfacealkalinity is measured by boiling in water for five minutes followed bytitration with 0.05 N HCl (ARMA Granule Test Method #7). The results areshown in Table 1. The use of aluminum fluoride, sodium silicofluoride,and Portland cement in the sodium silicate binder cured at a temperatureof 538 degrees C. (1000 degrees F.) results in much lower alkalinitynumber as compared to the control case. Also, several combinations ofthe ingredient with no clay result in a coating with a very lowalkalinity number, which is an indicative of complete insolubilizationof the binder and hence long-term durability.

TABLE 1 Kaolin Portland Cure Alka- Run Clay AlF₃ Na₂SiF₈ Cement WaterTemp. linity No. (g) (g) (g) (g) (g) (deg. F.) Number 1 0 0.705 0.2070.193 1.75 500 38.5 2 0 0.705 0.414 0.193 1.75 500 30.4 3 0 0.705 0.2070.385 1.75 500 36.5 4 3 0.705 0.207 0.193 3.75 500 28.5 5 0 1.41 0.2070.193 1.75 500 35.9 6 0 1.41 0.414 0.193 1.75 500 27.75 7 0 1.41 0.2070.385 1.75 500 33.5 8 3 1.41 0.193 0.193 3.75 500 27.8 9 0 0.705 0.4140.385 1.75 500 30.3 10 3 0.705 0.414 0.193 3.75 500 25.8 11 3 0.7050.207 0.385 3.75 500 30.7 12 3 0.705 0.414 0.385 3.75 500 20.6 13 3 1.410.414 0.385 3.75 500 20.75 14 0 1.41 0.414 0.385 1.75 500 28.6 15 3 1.410.414 0.193 3.75 500 25.8 16 3 1.41 0.207 0.385 3.75 500 25.6 17 0 0.7050.207 0.193 1.75 1000 10.05 18 0 0.705 0.414 0.193 1.75 1000 7.25 19 00.705 0.207 0.385 1.75 1000 8.9 20 3 0.705 0.207 0.193 3.75 1000 NA* 210 1.41 0.207 0.193 1.75 1000 4.9 22 0 1.41 0.414 0.193 1.75 1000 2.9 230 1.41 0.207 0.385 1.75 1000 1.5 24 3 1.41 0.207 0.193 3.75 1000 NA* 250 0.705 0.414 0.385 1.75 1000 4.3 26 3 0.705 0.414 0.193 3.75 1000 NA*27 3 0.705 0.207 0.385 3.75 1000 NA* 28 3 0.705 0.414 0.385 3.75 1000NA* 29 3 1.41 0.414 0.385 3.75 1000 NA* 30 0 1.41 0.414 0.385 1.75 10002.45 31 3 1.41 0.414 0.193 3.75 1000 NA* 32 3 1.41 0.207 0.385 3.75 1000NA*

EXAMPLES 2-4

Black colored roofing granules were prepared by coating 1000 g of inertmineral rocks suitable for shingle applications (commercially availablefrom CertainTeed Corp., Piedmont, Mo.), and a silicate coatingcomposition comprising 37.5 g of sodium silicate (grade 40, OccidentalChemical Co., Dallas, Tex.), 2.812 g of aluminum fluoride, 0.814 g ofsodium silicofluoride, 0.75 g of Portland cement, 0.6 g of green pigment(RD-1563 from Ferro Corp., Cleveland, Ohio), 0.46 g of ultramarine bluepigment (FP4O, also from Ferro Corp.), 4.4 g of black-pigment (10202black, also from Ferro Corp.), and 7 g of water. The coating compositionwas first mixed in a beaker with a mixer at 300 rpm and was then blendedwith the mineral particles in a plastic bottle until a uniform mixturewas attained. The coated granules were then dried by a fluidized beddryer, and were then heat treated at 496 degrees C. (925 degrees F.) ina rotary dryer to cure the coating composition. The resultant granuleshave a very dark color with L* at 26.55 and improved solar reflectance.Repeating the coating process for two additional layers of coatingprovided a color close to the typical dark black roofing granule knownas #51 black (Available from 3M Corp., Corona, Calif.) but having fourtimes higher solar reflectance. The results are listed in Table 2.

TABLE 2 Solar L* a* b* reflectance Control (#51 24.92 −0.12 −0.89 0.04black granule Example 2 26.55 2.01 2.63 0.14 (one coat) Example 3 25.430.81 1.18 0.17 (two coats) Example 4 24.14 0.42 0.84 0.20 (three coats)

Various modifications can be made in the details of the variousembodiments of the processes, compositions and articles of the presentinvention, all within the scope and spirit of the invention and definedby the appended claims.

The invention claimed is:
 1. A plurality of dark-colored roofinggranules, each of the dark-colored roofing granules comprising: an inertbase particle; and a cured coating disposed about the inert baseparticle, the cured coating being a reaction product of a coatingcomposition comprising: an alkali metal silicate; at least one non-claylatent heat reactant; and at least one inorganic solar heat-reflectivepigment, each of the at least one inorganic solar heat-reflectivepigments having an L* less than 30 and a solar reflectance greater than20 percent, and wherein the coating composition comprises at least about5 percent to 25 percent of the at least one solar heat-reflectivepigment, wherein the plurality of dark-colored roofing granules has anL* less than 30 and a solar reflectance greater than 20, and whereineach of the dark-colored roofing granules lacks a light-colored basecoat disposed between the inert base particle and the cured coating. 2.A plurality of dark-colored roofing granules according to claim 1,wherein in the coating composition the at least one non-clay latent heatreactant is selected from the group consisting of Portland cement,aluminum fluoride, ammonium silicofluoride, alkali metalsilicofluorides, and alkaline earth metal silicofluorides.
 3. Aplurality of dark-colored roofing granules according to claim 1, whereinin the coating composition the at least one non-clay latent heatreactant comprises Portland cement, aluminum fluoride and at least onealkali metal silicofluoride.
 4. A plurality of dark-colored roofinggranules according to claim 3, wherein in the coating composition the atleast one alkali metal silicofluoride is sodium silicofluoride.
 5. Aplurality of dark-colored roofing granules according to claim 3, whereinin the coating composition wherein the at least one non-clay latent heatreactant comprise from about 3 to 15 weight percent of the coatingcomposition of aluminum fluoride, from about 0.5 to 5 weight percent ofthe coating composition of sodium silicofluoride, and from about 0.5 to5 weight percent of the coating composition of Portland cement.
 6. Aplurality of dark-colored roofing granules according to claim 1, whereinin the coating composition wherein the at least one inorganic solarheat-reflective pigment is selected from the group consisting of ArcticBlack 10C909 (chromium green-black), Black 411 (chromium iron oxide),Brown 12 (zinc iron chromite), Brown 8 (iron titanium brown spinel), andYellow 193 (chrome antimony titanium), 56, Eclipse Black 10201, ForestGreen 10241, Eclipse Black 10202, Eclipse Black 10203, and H IR GreenV-12650.
 7. A plurality of dark-colored roofing granules of claim 1wherein in each of the dark-colored roofing granules the cured coatingcomprises a first layer including a first metal silicate binder and afirst inorganic solar heat-reflective pigment and a second layerincluding a second metal silicate binder and a second inorganic solarheat-reflective pigment.
 8. A plurality of dark-colored roofing granulesof claim 7 wherein in each of the dark-colored roofing granules thesecond inorganic solar heat-reflective pigment is identical to the firstinorganic solar heat-reflective pigment.
 9. A plurality of dark-coloredroofing granules of claim 8 wherein in each of the dark-colored roofinggranules the first and second inorganic solar heat-reflective pigmentsare selected from the group consisting of Arctic Black 10C909 (chromiumgreen-black), Black 411 (chromium iron oxide), Brown 12 (zinc ironchromite), Brown 8 (iron titanium brown spinel), and Yellow 193 (chromeantimony titanium), Brown 10364, Eclipse Black 10201, Forest Green10241, Eclipse Black 10202, Eclipse Black 10203, and H IR Green V-12650.10. A plurality of dark-colored roofing granules of claim 8 wherein ineach of the dark-colored roofing granules the first coating layercomprises at least about 30 percent to about 40 percent of the firstinorganic solar heat-reflective pigment, and wherein the second coatinglayer comprises at least about 30 percent to about 40 percent of thesecond inorganic solar heat-reflective pigment.
 11. A plurality ofdark-colored roofing granules of claim 7 wherein in each of thedark-colored roofing granules the first and second coating layers formfrom about 4 percent by weight of the inert base particle to about 10percent by weight of the inert base particle.
 12. A plurality ofdark-colored roofing granules of claim 7 wherein each of thedark-colored roofing granules further comprises a third coating layer,the third coating layer being identical to the second coating layer andthe first coating layer.
 13. A plurality of dark-colored roofinggranules of claim 7 wherein in each of the dark-colored roofing granulesthe second inorganic solar heat-reflective pigment is different from thefirst inorganic solar heat-reflective pigment.
 14. A plurality ofdark-colored roofing granules of claim 13 wherein in each of thedark-colored roofing granules the first inorganic solar heat-reflectivepigment is selected from the group consisting of Arctic Black 10C909(chromium green-black), Black 411 (chromium iron oxide), Brown 12 (zinciron chromite), Brown 8 (iron titanium brown spinel), and Yellow 193(chrome antimony titanium), Brown 10364, Eclipse Black 10201, ForestGreen 10241, Eclipse Black 10202, Eclipse Black 10203, and H IR GreenV-12650.
 15. A plurality of dark-colored roofing granules of claim 13wherein in each of the dark-colored roofing granules the secondinorganic solar heat -reflective pigment is selected from the groupconsisting of Arctic Black 10C909 (chromium green-black), Black 411(chromium iron oxide), Brown 12 (zinc iron chromite), Brown 8 (irontitanium brown spinel), and Yellow 193 (chrome antimony titanium), Brown10364, Eclipse Black 10201, Forest Green 10241, Eclipse Black 10202,Eclipse Black 10203, and H IR Green V-12650.
 16. A plurality ofdark-colored roofing granules of claim 13 wherein in each of thedark-colored roofing granules the second layer further comprises aninorganic solar-reflective functional pigment.
 17. A plurality ofdark-colored roofing granules of claim 16 wherein in each of thedark-colored roofing granules the solar-reflective functional pigment isselected from the group consisting of mirrorized silica flakes, metalflake pigments, and metal oxide coated flake pigments.
 18. A pluralityof dark-colored roofing granules of claim 16 wherein in each of thedark-colored roofing granules the second coating layer comprises atleast about 1 percent to about 60 percent of the solar-reflectivefunctional pigment.
 19. A plurality of dark-colored roofing granules ofclaim 16 wherein in each of the dark-colored roofing granules the secondcoating layer comprises at least about 1 percent to about 60 percent ofthe second solar heat-reflective pigment.
 20. A plurality ofdark-colored roofing granules of claim 1, wherein in each of thedark-colored roofing granules the inert base particle is an inertmineral particle and the cured coating is disposed directly on the inertmineral particle.
 21. A plurality of dark-colored roofing granules ofclaim 1, wherein in each of the dark-colored roofing granules thecoating composition further includes aluminum oxide having a particlesize in the range of 0.1 to 5 micrometers.
 22. A plurality ofdark-colored roofing granules of claim 1, wherein in each of thedark-colored roofing granules the coating composition is free of kaolinclay.
 23. A plurality of dark-colored roofing granules of claim 1,wherein in each of the dark-colored roofing granules the at least oneinorganic solar heat-reflective pigment is a metal oxide pigment.
 24. Aplurality of dark-colored roofing granules of claim 1, wherein in eachof the dark-colored roofing granules the at least one inorganic pigmentis the only pigment in the coating composition.
 25. A plurality ofdark-colored roofing granules of claim 1, wherein in each of thedark-colored roofing granules the inorganic solar heat-reflectivepigments does not comprise a white pigment coated with a nearinfrared-absorbing colorant.
 26. An asphalt shingle having a surfacecoated with the plurality of dark-colored roofing granules of claim 1,the shingle having an L* less than 55 and a solar reflectance of greaterthan 20 percent.
 27. An asphalt shingle having a surface coated with theplurality of dark-colored roofing granules of claim 1, the shinglehaving an L* less than 30 and a solar reflectance of greater than 20percent.